A silicon carbide (SiC) power semiconductor device is known as a device having excellent temperature and breakdown voltage characteristics. An electric field relaxation structure, which is called termination structure, is provided to a laterally outer edge of an active region of the power semiconductor device.
Known as a termination structure of the Schottky diode element—a kind of the power semiconductor device—is, for example, a junction termination extension (JTE) structure in which a region of conductivity different from that of a semiconductor region in the lower center of a Schottky electrode is provided in the semiconductor region of a perimeter of the Schottky electrode, and a dopant concentration in the termination structure is gradually reduced toward a circumference of the element (a literature such as Patent Document 1). Another structure is also known in which, in addition to a planar direction of the device, regions having plural dopant concentrations are provided also in a depth direction thereof, and a dopant sheet density of a termination structure is gradually reduced toward a circumference of the element (a literature such as Patent Document 2).
In order to form such a structure where the dopant concentration and the dopant sheet density are varied gradually, additional doping process such as ion implantation or epitaxial growth is performed. For that reason, the number of fabrication processes required for forming the structure having the dopant profile gradually varied needs to be undergone, resulting in some cases in an increase in the fabrication process. The increase in fabrication process leads to an increase in fabrication costs.
On the other hand, in a method of fabricating semiconductors, some attempts are known which form plural regions that are different in dopant concentration from each other, without increasing the number of photolithography processes. Among the known examples are: a method where when implanting ions into a semiconductor layer using a mask, the ion implantation is performed in a predetermined mask shape and with a predetermined density and thereafter by reducing the mask size and causing the mask to move backward, the ion implantation is performed with another density (Patent Document 3 and the like); a method where, by providing a portion where the ion implantation is performed through a film that partially passes ions therethrough, a region where the ion implantation is performed without passing through the film that partially passes the ions therethrough, and another region where a dopant concentration distribution varies in a depth direction, are formed simultaneously (a literature such as Patent Document 4); and a method where a stepped surface or a slanted cross-sectional shaped portion is provided to a mask, and dopants are ion implanted through this mask and thereafter the dopants are thermally diffused (a literature such as Patent Document 5).
Also known is an alignment mark having a slanted structure with a double stepped bottom (Patent Document 6, for example).